Field
The present invention relates to residual water scavenging processing in a fuel cell system.
Related Art
When the outside temperature is lowered below freezing point after the stop of an operation of a fuel cell system, in the interior of a unit cell forming a fuel cell (cell stack), a reaction gas flow path formed within the fuel cell, an external piping and the like, water may be frozen. When water is frozen in the fine pores of a catalyst layer and a gas diffusion layer within a unit cell, at the time of the subsequent startup of the fuel cell system, the gas diffusion property is lowered to reduce the power generation performance. When in a valve provided in the reaction gas flow path, water is frozen, the opening and closing of the valve is inhibited, and the distribution of a reaction gas and an off-gas is inhibited. Hence, a method has been proposed in which after the stop of a fuel cell system, the temperature of a fuel cell and the outside temperature are measured, and when these temperatures become equal to or less than a predetermined temperature, residual water scavenging processing is performed to discharge water within the fuel cell system. JP2010-198786A discloses a method in which when the ignition of a vehicle mounting the fuel cell system is off, and the temperature of a fuel cell is equal to or less than a predetermined temperature, residual water scavenging is performed on a fuel gas supply/discharge mechanism and an oxidizer gas supply/discharge mechanism. JP2008-218242A discloses a method in which when the outside temperature is measured during the stop of an operation of a fuel cell, and the outside temperature is equal or less than a predetermined temperature, residual water scavenging is performed on a fuel gas supply/discharge mechanism and an oxidizer gas supply/discharge mechanism.
It is assumed that in order to more reliably prevent water from being frozen within a fuel cell system, the two methods described above are combined, residual water scavenging processing is performed according to the temperature of a fuel cell when an ignition is off and the residual water scavenging processing is performed according to the outside temperature during the stop of the fuel cell system. However, in such a configuration, since the residual water scavenging processing is performed a large number of times, power consumption in devices performing the residual water scavenging processing such as an air compressor and the injector of hydrogen gas is disadvantageously increased. Moreover, in a case where the residual water scavenging processing is performed when an ignition is off, even though the ignition is off, vibrations and sound caused by the operation of the air compressor and the like are produced until the completion of the residual water scavenging processing, and thus an uncomfortable feeling is disadvantageously given to a user. Hence, a technology is desired in which it is possible to suppress the freezing of water within a fuel cell system while reducing power consumption necessary for residual water scavenging processing and the of an uncomfortable feeling to the use.